Limiting Factors Jigsaw
Background: The main factors affecting rate of photosynthesis are light intensity,
temperature, water availability, and wind speed. In any given situation any one of these
may become a limiting factor, in other words the factors that directly affects the rate at
which photosynthesis can take place masking the effects of the other factors.
Directions: Once you are assigned to an EXPERT group, you are to each read that
section and that section only. Take notes for that section of notes. Share the notes you
took with your EXPERT group and add anything new that you didn’t get that you feel is
important.
Go back to your HOME group and each of you will share what you have learned about
that limiting factor. Take notes on the other three sections and then complete the
worksheet.
Factors Affecting Photosynthesis
Expert Group 1: Sunlight
The Principle of Limiting Factors says that the maximum obtainable rate of
photosynthesis is limited by whichever basic resource of plant growth is in least
supply. There are 4 limiting factors for photosynthesis: Sunlight, Temperature,
Water Availability, and Wind Speed.
Sunlight is a requirement of photosynthesis. The plant must absorb energy
from sunlight to convert into energy in glucose. The more sunlight the plant has
available to it and the higher the light intensity, the more the chlorophyll can
absorb. Therefore as light intensity increases, the rate of photosynthesis increases.
Gradually the rate falls off and at a certain light intensity the rate levels out and
remains constant. At this point, carbon dioxide becomes the limiting factor- a plant
cannot photosynthesize if there is insufficient carbon dioxide because carbon
dioxide is a raw material for glucose synthesis.
Additionally, at a very high light intensity the rate of photosynthesis slows
down because the pigment chlorophyll is damaged by ultra-violet.
The reason is that the plant only has so many chloroplasts in the leaf to
absorb the sunlight at any given moment. To get the most sunlight possible, many
plants spread out their leaves in such a way that each leaf maximizes the amount
of light falling on them. The also spread them in a way that the lower leaves are
not shaded by the ones above.
Factors Affecting Photosynthesis
Expert Group 2: Temperature
The Principle of Limiting Factors says that the maximum obtainable rate of
photosynthesis is limited by whichever basic resource of plant growth is in least
supply. There are 4 limiting factors for photosynthesis: Sunlight, Temperature,
Water Availability, and Wind Speed.
Enzymes are necessary for the process of photosynthesis. Enzymes are
proteins that speed up chemical reactions. The more enzymes available and the
faster they move effects how fast a chemical reaction, such as photosynthesis, can
occur. As the temperature increases, molecules (enzymes) move faster, causing
molecules to collide more and have more reactions. Therefore, as temperature
increases, the rate of photosynthesis increases.
However, if the temperature rises above 40oC, the enzymes become
denatured. When an enzyme becomes denatured, its structure breaks down and it
doesn’t work properly. So, at higher temperatures, the rate of photosynthesis will
drop because the enzymes are denatured.
Not all plants have the same optimum temperature. Plants which grow in colder
climates have an optimum rate of photosynthesis at lower temperatures.
Greenhouses are used to capitalize on the effects of higher temperatures increasing
the rate of photosynthesis. Plants from regions of warmer climates can
successfully grow in colder regions by using greenhouses.
Additionally, high temperatures increase the rate of transpiration, leading to
the closure of the stomata. Closing the stomata can cause a build-up of oxygen
from photosynthesis in the leaves – and this reduces the rate of photosynthesis.
Factors Affecting Photosynthesis
Expert Group 3: Water Availability
The Principle of Limiting Factors says that the maximum obtainable rate of
photosynthesis is limited by whichever basic resource of plant growth is in least
supply. There are 4 limiting factors for photosynthesis: Sunlight, Temperature,
Water Availability, and Wind Speed.
Water is a reactant of photosynthesis and is necessary to make glucose in
the photosynthesis reaction. As water levels increase, the rate of photosynthesis
increases. With increased water, the stomata (pores on the underside of leaves) can
stay open and gases are exchanged to keep photosynthesis going. When there is
not enough water available to the plant, photosynthesis will slow and even stop
because transpiration increases. Transpiration is the process by which moisture is
carried through plants from roots to the stomata (small pores on the underside of
leaves), where it changes to vapor and is released to the atmosphere. Transpiration
is essentially evaporation of water from plant leaves. The stomata will eventually
close and the exchange of gases stops. However, at certain water levels, the rate of
photosynthesis levels out as other factors become limiting.
Water level is affected by precipitation and humidity. The more
precipitation falling in an environment, the more water there is in the ground for
the plant to take up through their roots for photosynthesis. Humidity is a measure
of water in the air. As humidity increases, the air becomes wetter, and less
transpiration occurs through the open stomata.
Factors Affecting Photosynthesis
Expert Group 4: Wind Speed
The Principle of Limiting Factors says that the maximum obtainable rate of
photosynthesis is limited by whichever basic resource of plant growth is in least
supply. There are 4 limiting factors for photosynthesis: Sunlight, Temperature,
Water Availability, and Wind Speed.
Moderate winds favor gas exchanges, but strong winds can cause excessive
water loss through transpiration as well as lodging or toppling of plants.
Transpiration is the process by which moisture is carried through plants from roots
to the stomata (small pores on the underside of leaves), where it changes to vapor
and is released to the atmosphere. Transpiration is essentially evaporation of water
from plant leaves. When transpiration rate exceeds that of water absorption, partial
or complete closure of the stomata may ensue which will restrict the diffusion of
carbon dioxide into the leaves. As a result, there will be a decrease in the rate of
photosynthesis, growth and yield.
As wind speed increases, it dries out the air (reduces humidity). Therefore
at high wind speeds, transpiration increases. If the leaf dries out too much, the
stomata shut and photosynthesis slows or stops. As long as other factors are not
limiting, slower winds will not affect humidity. So, the rate of photosynthesis will
rise slightly at lower wind speeds and then slow and drop off as wind speed
increases.
Additionally wind carries oxygen away from the plant. Less wind, less
evaporation, less water requirement. Wind may aid in pollination, interfere with
farm operations such as spraying crops, and may blow away pests and diseases
thus carry pests to or away from crop.
Factors Affecting Photosynthesis
For each factor, fill in the graph to show how that factor affects photosynthesis.
Sunlight
Temperature
Rate of
Rate of
Photosynthesis
Photosynthesis
Light Intensity
Temperature
Water
Wind Speed
Rate of
Rate of
Photosynthesis
Photosynthesis
Water Availability
Wind Speed
For each scenario, predict the effect on photosynthesis.
Scenario 1: Sunlight becomes less direct in autumn. Affect: INCREASE, DECREASE, STAY
THE SAME- Justification (complete sentences):
______________________________________________________________________________
______________________________________________________________________________
Scenario 2: Plant experiences severe drought. Affect: INCREASE, DECREASE, STAY THE
SAME- Justification (complete sentences):
______________________________________________________________________________
______________________________________________________________________________
Scenario 3: Wind speed increases. Affect: INCREASE, DECREASE, STAY THE SAMEJustification (complete sentences):
______________________________________________________________________________
______________________________________________________________________________
Scenario 4: Temperature lowers from 30oC to 10oC. Affect: INCREASE, DECREASE, STAY
THE SAME- Justification (complete sentences):
______________________________________________________________________________
______________________________________________________________________________